The term "separation" refers to the point at which patients on TEV-48125 started to improve, compared to patients given a placebo (an inactive treatment).

TEV-48125 is one of a new class of drugs being developed to prevent migraines. The medications are all antibodies that block a chemical in the nervous system called CGRP. Research has found that CGRP causes inflammation and blood vessel dilation, and it spikes in the brain during migraine attacks.

Dr. Mark Green is professor of neurology and anesthesiology at the Mount Sinai Icahn School of Medicine, in New York City. "It appears that this antibody works quite quickly," said Green, who is also director of the Center for Headache and Pain Medicine at Mount Sinai.

Green, who was not involved in the study, called the findings "exciting." That's in part because if CGRP-blockers make it to the market, they would be the first drugs specifically designed to prevent migraines.

About 12 percent of Americans suffer from migraines, according to the U.S. National Institutes of Health. The headaches typically cause an intense throbbing pain on one side of the head, and sensitivity to light and sound. Some people have nausea, too.

Migraines are considered chronic when they strike at least 15 days out of the month, the study authors said.

Doctors prescribe various medications that can help prevent frequent migraines -- including certain blood pressure drugs, antidepressants and Botox injections. But, Green pointed out, all of those drugs were originally designed to treat other conditions. Over the years, doctors have found that they can also reduce migraines in some people.

And of those drugs, Botox is the only one that is actually approved for preventing migraines, Green said.

When Botox works, it typically takes two or three rounds of injections for patients to start seeing the benefit, according to Green. And those treatments are done at three-month intervals. So some patients give up on it, he said.

The oral medications used for migraine prevention kick in faster -- typically four to six weeks. But they are also daily pills with potential side effects, such as weight gain, dizziness and fatigue (depending on the medication), Green said.

The new study findings come from a reanalysis of an early trial of TEV-48125. In that study, more than 250 patients with chronic migraine were randomly assigned to take monthly injections of the drug -- at a higher or lower dose -- or a placebo, for three months.

The original study found that patients on TEV-48125 saw a drop in the number of hours they had headache pain each month.

On average, the whole study group had 162 "headache hours" a month when it started the study. Three months later, that had dropped by 60 to 67 hours, on average, among patients on the new drug.

The new study found that the effects started as early as three days after the higher-dose injection, and seven days after the lower dose.

So far, Green said, there have been "no significant safety signals" with the drug. In the original study, the most common side effects were pain at the injection site and skin irritation.

But it's still early, Green stressed.

Bigal said ongoing studies will keep looking at the drug's safety. "No treatment-related serious adverse events have been seen so far," he said.

If TEV-48125 or its competitors are approved, it's unlikely that patients will be put off by having to take a monthly injection, according to Green.

"These are people in chronic pain," he pointed out.

But cost could be an obstacle: In general, antibody drugs like TEV-48125 are very expensive. So patients might find it difficult to get insurance coverage, Green said.